### The Story of SAOImageDS9: How DS9 got its name

> In 1990, Mike Van Hilst, at the Smithsonian Astrophysical Observatory, Center for Astrophysics, Harvard University, developed SAOImage. SAOImage was first implemented in X10, then reimplemented in X11. In fact, it was one of the first X11 based applications publicly made available. SAOImage was a brilliant program, implementing techniques in scientific visualization 20 years ago that are still being used by today's applications. Since Mike's departure from SAO, SAOImage has been maintained by Jessica Mink.

> In the mid 1990's, with the administrative support of Steve Murray, Eric Mandel developed SAOtng, or (SAOImage, The Next Generation), named after the Star Trek series. TNG was based on IRAF's XIMTOOL graphics libraries and Tcl. It explored new GUI interfaces and supported a new external analysis interface. In particular, it utilized XPA, (X11 Public Access, also written by Eric) which allowed TNG to be scripted via a shell, or from other application.

> In 1998, while working with Eric, William Joye began a complete rewrite of TNG, based on the experience developed while supporting TNG. This project was funded by the NASA Applied Information Systems Research Program, under the title "Future Directions for Astronomical Image Display". For lack of a name, the new project was referred to as DS9, the logical extension of the Star Trek series. The name continues to be in use. Current funding is provided by the NASA High Energy Astrophysics Science Archive Center and the Chandra X-ray Science Center.

> DS9 is a Tcl/Tk application. The GUI is implemented as a very thin layer of Tk. A number of Tk Canvas widgets in C++ were created to support all the functionality needed. Basically, all the real work is done in C++. DS9 inherited TNG's support of regions, XPA, external analysis support, and the general GUI. However, all the visualization techniques come directly from SAOImage.

> The current version of DS9 is composed of the Tk widgets created along with support from about 20 other open source products (including Tcl/Tk, AST, BLT, HCompress, HTMLWidget, plio, rics, tcllib, tclxml, tkcon, tkimg, tktable, wcssubs, xmlrpc, XPA, zip, zlib, and zvfs). The distributed binaries consist of a self-contained self-extracting archive and application, which provides an independent Tcl/Tk environment without installation.

> The first versions of DS9 were made available in 1999. Since then, the popularity of DS9 has grown far beyond expectations.